1. Field of the Invention
The present invention relates to an intake air control device for an internal combustion engine.
2. Description of the Related Art
The amount of the intake air is normally controlled by a throttle valve mechanically connected to an accelerator pedal. It is known to provide a intake air control means operable in response to the running condition of the engine, other than such a manually operated throttle valve. For example, a supercharger is provided, which is connected to an output shaft of the engine via a solenoid clutch, which is activated to operate the supercharger when the load of the engine is high (c.f., for example, Japanese Unexamined Patent Publication Nos. 59-18227 and 59-28004). Alternatively, a second valve may be provided on the downstream side of the throttle valve, which is opened to improve the volumetric efficiency of the air sucked into the engine when the load or the speed of the engine is high.
It is necessary, in a fuel injection type of internal combustion engine, to inject the fuel at a constant pressure relative to the pressure in the intake air pipe, and thus an electrically operated fuel pump is used in such an engine.
The electrically operated fuel pump is designed so that it discharges a substantially constant output flow and receives a constant voltage from the battery. Nevertheless, there is a problem in that, as can be seen from FIG. 6 of the attached drawings, the output flow from the pump may drop if the voltage of the battery drops. A drop in the voltage of the battery may occur, for example, when lights and several electric auxiliary machines are used at the same time. Conventionally, taking this voltage drop into account, a fuel pump having an unnecessarily large capacity, capable of obtaining a sufficient output flow even under the reduced voltage, has been used. Further, the fuel consumption is remarkably increased when the load and speed of the engine is high, thus the capacity of the fuel pump must be further enlarged to ensure that the fuel delivery from the fuel pump may not become too low if the voltage drop occurs under this situation. Therefore, it is necessary to fit a relatively large, and thus expensive, fuel pump in an internal combustion engine.